Traditionally, camera cranes and dollies have been employed to assist in the positioning of cameras at defined locations and orientations to capture the desired shot. Conventional camera cranes are generally comprised of a crane arm (or “jib”), a support structure to which the crane arm is mounted, and a “leveling head” affixed to the distal end of the crane arm. Typically, the crane arm is pivotally coupled to the support structure in a manner that facilitates the rotation of the crane arm about a vertical and a horizontal axis. The rotation of the crane arm about the vertical axis is generally referred to as crane arm “swing,” while the rotation of the crane arm about the horizontal axis is generally referred to as crane arm “boom.” In addition to the crane arm being capable of swing and boom, conventional crane arms are often constructed to be adjustable in length, so that the crane arm can “telescope” from one length to another. Thus, the distal end of the crane arm (i.e., the end affixed to the leveling head) is capable of translating through a semi-sphere, the diameter of which is controlled by the overall length of the crane arm, which can be adjusted by telescoping the crane arm. Moreover, camera cranes are often mounted on a rolling platform that is generally referred to as a “dolly.”
Conventional camera dollies are different from the dollies used to support camera cranes mentioned above, in that instead of supporting a complex crane arm that can swing, boom and telescope, conventional camera dollies support a simpler camera platform which may only be raised or lowered. Conventional camera dollies exist in two basic forms, and typically employ wheels for movement. Some dollies have rectangular-shaped frames with a steering lever at the back, and others are symmetrical and steerable from any side. The camera platform is provided on the dolly for mounting a camera, and is typically supported by a single or double hinged arm which raises or lowers the platform using a hydraulic ram. Other dollies provide vertical movement using a hydraulic center post. In either case, the platform is raised in a vertical direction with respect to the frame of the dolly, and a leveling mechanism may be employed within the arm or post to maintain the platform level with respect to the frame of the dolly.
In a modern dolly, several modes of steering may be available. In a “conventional” mode of steering, the back wheels turn and the front wheels are fixed, or vice versa. In another mode of steering, called a “crab” mode, all four wheels turn together in parallel. In a “modified crab” mode, the front wheels turn together, and the back wheels turn together, but the front and back wheels are not necessarily parallel (typically the front wheels turn more than the back wheels). In yet another mode of steering called a “roundy” mode, the wheels are oriented so that the dolly can spin in place. Some dollies are configured for only one of these modes. By moving a lever on the dolly, other dollies are configurable into one of these modes.
Dollies are typically pushed and steered, and their platforms raised and lowered, by a dolly grip. Even though the technology exists to control the dolly remotely, it is difficult to replace the human element of an experienced dolly grip, who is able to watch a scene being performed and position and move the dolly while anticipating and compensating for deviations from the planned rehearsed movements of the actors. Moreover, dolly grips generally move at the same rate as actors, unlike joysticks and computer controls, which can move abruptly, and are thus generally better than remote controls at compensating for movements of actors.
The leveling head is a mechanism that is typically employed to connect the camera crane arm to a camera mounting structure referred to as a “camera head.” Leveling heads are generally comprised of a leveling mechanism that functions to maintain a “leveling plate” parallel to a defined plane in response to changes in the boom of the crane arm. As used in this application a “leveling plate” is a defined member of the leveling head that is adapted to being coupled to the camera head. An example of such a leveling head is disclosed in U.S. Pat. No. 4,943,019, which is hereby incorporated by reference.
Conventional camera heads, in addition to providing a support structure to securely mount the camera, are typically adapted to rotate about a vertical axis (i.e., panning) and a horizontal axis (i.e., tilting) relative to the leveling plate. To facilitate the panning and tilting of the camera head, two independently actuated motor mechanisms are usually employed. The first is often referred to as a “camera pan motor,” which as the name suggests facilitates the panning of the camera head (i.e., the rotation of the camera head about the vertical axis). The second is often referred to as a “camera tilt motor,” which also as the name suggests facilitates the tilting of the camera head (i.e., the rotation of the camera head about the horizontal axis).
In operation, the boom (i.e., the rotation of the crane arm about a horizontal axis), swing (i.e., the rotation of the crane arm about a vertical axis), telescope (i.e., the length of the crane arm), and the movement of the rolling platform or dolly are typically controlled manually by one or more operators or “grips.” The adjustments of the leveling head are usually automated to respond to the change in the boom so as to maintain the camera head generally level to the horizontal plane. The “pan” and “tilt” of the camera head together with the focus of the camera, on the other hand, have been traditionally controlled remotely (usually via electrical circuitry) by another operator, referred to as the “camera-operator,” who is responsible for the composition of the shot (i.e., the field of view and focus of the camera).
Thus, the camera-operator, in fashioning the composition of the shot, must compensate the field of view of the camera by panning and tilting the camera head in response to movements of the crane arm, dolly, and the subject matter being filmed. In light of the complex dynamics of such systems, the camera-operator's task can be extremely difficult, especially when filming complicated shots. Consequently, situations inevitably arise where the field of view of the camera is not accurately or in a timely fashion compensated for the movements of the crane arm and/or dolly. In addition, situations also arise, with or without movement in the camera crane or dolly, where the field of view of the camera is not accurately compensated for the movement of the subject matter. As a result, considerable expense and time is expended in re-shooting.
To assist the camera operator in achieving the desired composition, some camera heads such as those disclosed in U.S. Pat. Nos. 5,644,377 and 5,835,193, which are hereby incorporated by reference, employ an automated back pan compensation mechanism that, when activated, pans the camera head in a reverse direction relative to the swing of the camera crane arm. The amount of pan compensation may be adjusted by the user prior or during filming. These compensation mechanisms, however, simply reverse pan the camera head in response to changes in the swing of the crane arm without reference to the other potential movements of the camera support structure (e.g., boom, telescope, or dolly movement) or changes in the position of the subject matter being filmed. Furthermore, these compensation mechanisms are not readily suited for achieving accurate back pan compensation in response to changes in the swing of the crane arm. This is so because there is non-linear relationship between changes in the angular position of the camera arm and the desired angular back pan of the camera head. Thus, these systems require adjustment/calibration of the back pan gain, especially when large changes in the swing of crane arm occur. Consequently, these compensation mechanisms, while potentially helpful in assisting the camera operator in panning the camera head in certain circumstances, may not provide suitable assistance in situations in which the movement of the camera support structure is more complex or when a change in the position of the subject matter occurs.